Pgs Geophysical As

Okwudili Chuks Orji

Walter Söllner

Endrias Getachew Asgedom

Mattias Dan Christian Oscarsson

Nils Lunde

Stian Hegna

Elsa Cecconello

Daniel Martin Lewis Barker

Mickael Bastard

Endrias Getashew Asgedom

A proposed geometrical distribution for a first non-impulsive source and a second non-impulsive source of a source array can be received. A near-field-to-notional computation can be performed for the proposed geometrical distribution to yield a respective computed notional output of the first and second non-impulsive sources. Whether the computed notional output of the first non-impulsive source has a first amount of residue greater than a threshold amount of residue can be determined. Whether the computed notional output of the second non-impulsive source has a second amount of residue greater than the threshold amount of residue can be determined. An indication whether either of the first or second amounts of residue is less than or equal to the threshold amount of residue can be provided.

Geometrical distribution for non-impulsive sources

Processes and systems described herein are directed to performing marine surveys with marine vibrators that emit orthogonal coded pseudo-random sweeps. In one aspect, coded pseudo-random signals are generated based on coded pseudo-random sequences. The coded pseudo-random sequences are used to activate the marine vibrators in a body of water above a subterranean formation. The activated marine vibrators generate orthogonal coded pseudo-random sweeps. A wavefield emitted from the subterranean formation in response to the orthogonal coded pseudo-random sweeps is detected at receivers located in a body of water. Seismic signals generated by the receivers may be cross-correlated with a signature of one of the orthogonal coded pseudo-random sweeps to obtain seismic data with incoherent residual noise.

Mitigating residual noise in a marine survey with orthogonal coded pseudo-random sweeps

Processes and systems described herein are directed to imaging a subterranean formation from seismic data recorded in a marine survey with moving marine vibrators. The marine vibrators generate random sweeps with random sweep signatures. Processes and systems generate an up-going pressure wavefield from measured pressure and vertical velocity wavefield data recorded in the marine survey and obtain a downgoing vertical acceleration wavefield that records source wavefields, directivity, source ghosts, and random signatures of the random sweeps. The downgoing vertical acceleration wavefield data is deconvolved from the up-going pressure wavefield to obtain a subsurface reflectivity wavefield that is used to generate an image of the subterranean formation with reduced contamination from source wavefields, directivity, source ghosts, and random signatures of the random sweeps.

Seismic imaging with source deconvolution for marine vibrators with random source signatures

Methods and systems to separate seismic data associated with impulsive and non-impulsive sources are described. The impulsive and non-impulsive sources may be towed through a body of water by separate survey vessels. Receivers of one or more streamers towed through the body of water above a subterranean formation generate seismic data that represents a reflected wavefield produced by the subterranean formation in response to separate source wavefields generated by simultaneous activation of the impulsive source and the non-impulsive source. Methods and systems include separating the seismic data into impulsive source seismic data associated with the impulsive source and non-impulsive source seismic data associated with the non-impulsive.

Methods and systems to separate seismic data associated with impulsive and non-impulsive sources

Processes and systems are described for generating an image of a subterranean formation from seismic data recorded during a marine survey that employed a moving vibrational source. Processes and systems compute an up-going pressure wavefield from pressure data and vertical velocity data recorded in the marine survey. A direct incident downgoing vertical velocity wavefield that includes Doppler effects created by the moving vibrational source and characterizes a source wavefield and source ghost of the moving vibrational source is computed and deconvolved from the upgoing pressure wavefield to generate a subsurface reflectivity wavefield. The subsurface reflectivity wavefield is effectively free of contamination from the source wavefield, the source ghost, and the Doppler related effects. Processes and systems generate an image of the subterranean formation based on the subsurface reflectivity wavefield, thereby enhancing resolution of the image by attenuating the source-motion effects, source signature, and source ghost of the moving vibration source.

Correction of source motion effects in seismic data recorded in a marine survey using a moving source

Survey design for data acquisition using marine non-impulsive sources can include operating a first marine non-impulsive source at over a first frequency range for a first sweep length and operating a second marine non-impulsive source over a second frequency range for a second sweep length. The first sweep length can be based on available geological information of a subsurface location that is a target of a marine seismic survey, an intended speed of a marine survey vessel, and the first frequency range. The second sweep length can be based on the available geological information, the intended speed, and the second frequency range.

Survey design for data acquisition using marine non-impulsive sources

Parameters of a sweep signal that controls operation of a marine non-impulsive source can be set. Setting the parameters can include selecting a stop frequency of the sweep signal, defining a taper of the sweep signal, and adjusting an initial phase of the sweep signal. The parameters can be set such that a magnitude of an amplitude spectrum of a combined output of a marine impulsive source and the marine non-impulsive source is greater than or equal to a magnitude of an amplitude spectrum of a marine impulsive source output at frequencies below the stop frequency. A controller of the marine non-impulsive source can be programmed with the sweep signal having the parameters set to control the marine non-impulsive source.

Sweep signal for combination of a marine non-impulsive source output with a marine impulsive source output

Determining a far field signature of a source array can include receiving data associated with a sea surface state and determining a coherent portion and an incoherent portion of a reflection coefficient of the sea surface based on the received data. A notional source signature of each source of the source array can be determined based on the coherent portion, the incoherent portion, and near field data associated with each of the sources, and the far field signature of the source array can be determined based on the notional source signatures of each of the sources. The notional source signature and the far field signature can be stored. A seismic image of a subsurface location can be generated based on the determined far field signature.

Far field signature determination

The current disclosure is directed to methods and systems to determine properties of a subterranean formation located below a body of water. The methods and systems compute synthetic pressure and velocity vector wavefields that represent acoustic energy interactions within a model environment that comprises a model body of water located above a model subterranean formation. The model environment is separated into a stationary region and a time-varying region. The methods and systems include determining properties of the subterranean formation by iteratively adjusting the model environment to approximate the actual subterranean formation. The model environment is iteratively adjusted until a minimum difference between the synthetic pressure and velocity vector wavefields computed for each change to the model environment and actual pressure and velocity wave fields obtained from a marine seismic survey of the subterranean formation is achieved.

Methods and systems to determine properties of a subterranean formation

Methods and systems that compute an approximate vertical-velocity wavefield based on a measured pressure wavefield and knowledge of the free-surface shape when the pressure wavefield was measured are described. The measured pressure wavefield is used to compute an approximate frozen free-surface profile of the free surface. The approximate frozen free-surface profile and the measured pressure wavefield are then used to compute an approximate vertical-velocity wavefield that does not include low-frequency streamer vibrational noise. The approximate vertical-velocity wavefield and measured pressure wavefield may be used to separate the pressure wavefield into up-going and down-going pressure wavefields.

Methods and systems that determine a velocity wavefield from a measured pressure wavefield

Marine survey data resulting from a first signal comprising a signal representing a flat spectral far-field pressure generated by a marine vibrator source swept over a frequency range according to a time function of motion such that acceleration of the marine vibrator source is a flat function in a frequency domain can be used to improve full waveform inversion. For example, full waveform inversion can be performed using the marine survey data received from the first signal and from a second signal generated by an impulsive seismic source to estimate a physical property of a subsurface location.

Marine vibrator source acceleration and pressure

Methods and systems that remove particle-sensor noise from measured vertical-velocity wavefield are presented. A approximate vertical-velocity data is computed from pressure data and vertical-velocity data at receiver coordinates of a seismic data acquisition system. The pressure data is composed of a pressure signal component and pressure-sensor noise and the vertical-velocity data is composed of a vertical-velocity signal component and particle-motion-sensor noise. A filter that gives a minimum difference between the vertical-velocity data and the approximate vertical-velocity data at each receiver coordinate is computed. Vertical-velocity data composed of the vertical-velocity signal component and approximate particle-motion-sensor noise based on the pressure-sensor noise is convolved with the filter at each receiver coordinate.

Methods and systems to remove particle-motion-sensor noise from vertical-velocity data

This disclosure is directed to wavefield separation methods and systems. In one aspect, methods and systems compute an approximate vertical particle velocity wavefield based on a measured pressure wavefield and knowledge of free-surface when the pressure wavefield was measured. The measured pressure wavefield is used to compute an approximate frozen free-surface profile. The approximate frozen free-surface profile and the measured pressure wavefield are used to compute an approximate vertical particle velocity wavefield. The approximate vertical particle velocity wavefield and measured pressure wavefield may be used to compute separate up-going and down-going pressure, or vertical particle velocity, wavefields.

Methods and systems to separate wavefields using pressure wavefield data

Computational methods and systems for deghosting marine seismic streamer data are described. In particular, an exploration-seismology vessel tows a number of streamers that form a data acquisition surface located beneath a free surface. The methods computationally deghost or substantially remove receiver ghost signals from seismic data recorded by steamer receivers. The deghosting methods include low frequency compensation to recover vertical velocity wavefield information that is typically lost due to a low signal-to-noise ratio over a low frequency range independent of the free surface conditions or the shape of the data acquisition surface.

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Oslo, Norway

Okwudili Chuks Orji